This invention relates to marine risers for deep subsea drilling and production and in particular to a coupling assembly therefor.
Marine risers are run from floating vessels or platforms to subsea wellheads for drilling and production operations. The riser sections are tubular, in the order of 20 inches in diameter and fifty feet long. These are assembled at the surface and run from the vessel or platform to a subsea wellhead.
The riser is usually highly tensioned at its upper end to avoid buckling, and is also subject to bending caused by water currents and/or vessel drift. These bending forces are cyclical and therefore have the potential of causing fatigue failure of riser components. The bending not only places the bolts on the tension side of a flanged connector assembly in tension but flange deflection and rotation causes bending of the bolts. The bending of these bolts is of concern since they are not only normally highly loaded but being threaded they have inherent stress concentration locations where this high cyclical stress occurs.